Nematic phases observed in amphiphilic polyelectrolyte-surfactant aggregate solutions

A lyotropic phase transition is observed in a water-soluble polyelectrolyte-surfactant aggregate system (polymerized cetyltrimethylammonium 4-vinylbenzoate, or pC16TVB). Unlike other oppositely-charged polyelectrolyte-surfactant aggregates at the stoichiometrically-matched charge point, these aggregates do not precipitate, and instead form isotropic-nematic biphasic solutions in water. The aggregates maintain amphiphilic behavior through the phase transition and appear to maintain the structure observed in dilute solution - that of rod-like aggregates (L/d ∼ 35 with d = 4 nm). Rheology, microscopy and small-angle neutron scattering are used to verify the nature of the phase transition and structure of the mesogen. The phase transition occurs at a concentration higher than that predicted by simple theory; however, flexibility, charge repulsion and polydispersity must be considered in this system.